This patch changes the anon_vma refcount to be 0 when the object is free. It does this by adding 1 ref to being in use in the anon_vma structure (iow. the anon_vma->head list is not empty). This allows a simpler release scheme without having to check both the refcount and the list as well as avoids taking a ref for each entry on the list. Signed-off-by: Peter Zijlstra --- include/linux/rmap.h | 11 +++++-- mm/ksm.c | 4 -- mm/rmap.c | 79 ++++++++++++++++++--------------------------------- 3 files changed, 38 insertions(+), 56 deletions(-) Index: linux-2.6/include/linux/rmap.h =================================================================== --- linux-2.6.orig/include/linux/rmap.h +++ linux-2.6/include/linux/rmap.h @@ -73,7 +73,13 @@ static inline void get_anon_vma(struct a atomic_inc(&anon_vma->refcount); } -void put_anon_vma(struct anon_vma *); +void __put_anon_vma(struct anon_vma *anon_vma); + +static inline void put_anon_vma(struct anon_vma *anon_vma) +{ + if (atomic_dec_and_test(&anon_vma->refcount)) + __put_anon_vma(anon_vma); +} static inline struct anon_vma *page_anon_vma(struct page *page) { @@ -116,7 +122,6 @@ void unlink_anon_vmas(struct vm_area_str int anon_vma_clone(struct vm_area_struct *, struct vm_area_struct *); int anon_vma_fork(struct vm_area_struct *, struct vm_area_struct *); void __anon_vma_link(struct vm_area_struct *); -void anon_vma_free(struct anon_vma *); static inline void anon_vma_merge(struct vm_area_struct *vma, struct vm_area_struct *next) @@ -125,6 +130,8 @@ static inline void anon_vma_merge(struct unlink_anon_vmas(next); } +struct anon_vma *page_get_anon_vma(struct page *page); + /* * rmap interfaces called when adding or removing pte of page */ Index: linux-2.6/mm/ksm.c =================================================================== --- linux-2.6.orig/mm/ksm.c +++ linux-2.6/mm/ksm.c @@ -309,9 +309,7 @@ static void hold_anon_vma(struct rmap_it static void ksm_put_anon_vma(struct rmap_item *rmap_item) { - struct anon_vma *anon_vma = rmap_item->anon_vma; - - put_anon_vma(anon_vma); + put_anon_vma(rmap_item->anon_vma); } /* Index: linux-2.6/mm/rmap.c =================================================================== --- linux-2.6.orig/mm/rmap.c +++ linux-2.6/mm/rmap.c @@ -67,11 +67,24 @@ static struct kmem_cache *anon_vma_chain static inline struct anon_vma *anon_vma_alloc(void) { - return kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL); + struct anon_vma *anon_vma; + + anon_vma = kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL); + if (anon_vma) { + atomic_set(&anon_vma->refcount, 1); + /* + * Initialise the anon_vma root to point to itself. If called from + * fork, the root will be reset to the parents anon_vma. + */ + anon_vma->root = anon_vma; + } + + return anon_vma; } -void anon_vma_free(struct anon_vma *anon_vma) +static inline void anon_vma_free(struct anon_vma *anon_vma) { + VM_BUG_ON(atomic_read(&anon_vma->refcount)); kmem_cache_free(anon_vma_cachep, anon_vma); } @@ -133,11 +146,6 @@ int anon_vma_prepare(struct vm_area_stru if (unlikely(!anon_vma)) goto out_enomem_free_avc; allocated = anon_vma; - /* - * This VMA had no anon_vma yet. This anon_vma is - * the root of any anon_vma tree that might form. - */ - anon_vma->root = anon_vma; } anon_vma_lock(anon_vma); @@ -156,7 +164,7 @@ int anon_vma_prepare(struct vm_area_stru anon_vma_unlock(anon_vma); if (unlikely(allocated)) - anon_vma_free(allocated); + put_anon_vma(allocated); if (unlikely(avc)) anon_vma_chain_free(avc); } @@ -237,9 +245,9 @@ int anon_vma_fork(struct vm_area_struct */ anon_vma->root = pvma->anon_vma->root; /* - * With KSM refcounts, an anon_vma can stay around longer than the - * process it belongs to. The root anon_vma needs to be pinned - * until this anon_vma is freed, because the lock lives in the root. + * With refcounts, an anon_vma can stay around longer than the + * process it belongs to. The root anon_vma needs to be pinned until + * this anon_vma is freed, because the lock lives in the root. */ get_anon_vma(anon_vma->root); /* Mark this anon_vma as the one where our new (COWed) pages go. */ @@ -249,7 +257,7 @@ int anon_vma_fork(struct vm_area_struct return 0; out_error_free_anon_vma: - anon_vma_free(anon_vma); + put_anon_vma(anon_vma); out_error: unlink_anon_vmas(vma); return -ENOMEM; @@ -268,15 +276,11 @@ static void anon_vma_unlink(struct anon_ list_del(&anon_vma_chain->same_anon_vma); /* We must garbage collect the anon_vma if it's empty */ - empty = list_empty(&anon_vma->head) && !atomic_read(&anon_vma->refcount); + empty = list_empty(&anon_vma->head); anon_vma_unlock(anon_vma); - if (empty) { - /* We no longer need the root anon_vma */ - if (anon_vma->root != anon_vma) - put_anon_vma(anon_vma->root); - anon_vma_free(anon_vma); - } + if (empty) + put_anon_vma(anon_vma); } void unlink_anon_vmas(struct vm_area_struct *vma) @@ -1441,38 +1445,11 @@ int try_to_munlock(struct page *page) return try_to_unmap_file(page, TTU_MUNLOCK); } -/* - * Drop an anon_vma refcount, freeing the anon_vma and anon_vma->root - * if necessary. Be careful to do all the tests under the lock. Once - * we know we are the last user, nobody else can get a reference and we - * can do the freeing without the lock. - */ -void put_anon_vma(struct anon_vma *anon_vma) -{ - BUG_ON(atomic_read(&anon_vma->refcount) <= 0); - if (atomic_dec_and_lock(&anon_vma->refcount, &anon_vma->root->lock)) { - struct anon_vma *root = anon_vma->root; - int empty = list_empty(&anon_vma->head); - int last_root_user = 0; - int root_empty = 0; - - /* - * The refcount on a non-root anon_vma got dropped. Drop - * the refcount on the root and check if we need to free it. - */ - if (empty && anon_vma != root) { - BUG_ON(atomic_read(&root->refcount) <= 0); - last_root_user = atomic_dec_and_test(&root->refcount); - root_empty = list_empty(&root->head); - } - anon_vma_unlock(anon_vma); - - if (empty) { - anon_vma_free(anon_vma); - if (root_empty && last_root_user) - anon_vma_free(root); - } - } +void __put_anon_vma(struct anon_vma *anon_vma) +{ + if (anon_vma->root != anon_vma) + put_anon_vma(anon_vma->root); + anon_vma_free(anon_vma); } #ifdef CONFIG_MIGRATION -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/